Catechols are defined as members of a family of aromatic diols having a substituted 1,2-benzenediol skeleton. Tiron, also known as 1,2-dihydroxybenzene-3,5-disulfonic acid, is one member of the catechol family and has the molecular structure shown in Scheme 1. Other sulphonated catechols also exist. In addition to the disulfonic acid, the term “tiron” may also include mono- or di-sulfonate salts of the acid, such as, for example, the disodium sulfonate salt.

Tiron and other catechols bind to ions of certain transition metals, such as ions of iron and titanium, and form colored metal/chelant complex. For example, in solutions tiron binds to ferric iron (Fe3+) to form a burgundy red metal/tiron complex. The presence of this colored Fe3+/tiron species may be detected at metal ion concentrations of 0.1 parts per million (ppm) or even lower. Thus, tiron has traditionally been used as a colorimetric indicator/chelant for the presence of titanium or iron.
Catechols, such as tiron, are also small molecule chelants that may be used as cleaning agents. For example, tiron delivers robust hydrophilic cleaning benefits and may also drive particulate cleaning via clay peptization, suspension, and/or synergy with polymeric dispersing systems. In addition, tiron may be compatible with certain enzymatic cleaning agents used in certain detergent compositions.
However, many detergent compositions contain low concentrations of soluble iron, such as ferric iron. The concentration of ferric iron in these detergents is enough to form sufficient metal/chelant complexes with certain catechols, such as tiron, to give the detergent an undesirable reddish color. This is particularly true for liquid detergent compositions in which the soluble ferric iron may freely complex with the tiron in the liquid detergent. For example, addition of low levels of tiron to commercially available detergents results in the detergent acquiring a reddish hue associated with the formation of the iron/tiron complex.
Many consumers may disfavor reddish colored detergents. For example, a reddish color in detergent may be associated with rust. Thus, in order to allow production of detergent compositions within the broadest possible color space, many detergent producers specifically avoid red chromophores. The presence of red chromophores in a detergent formulation may result in additional cost required to remove the red color from the detergent. Since detergents comprising certain catechols, such as tiron, would result in a reddish hue to the detergent composition due to the presence of ferric iron, many catechols, including tiron, have not traditionally been used in detergent applications, particularly in liquid detergents.
It would be desirable to produce a detergent possessing the cleaning benefits associated with tiron without the concomitant formation of the reddish iron/chelate complex.